copydir.c

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/*-------------------------------------------------------------------------
 *
 * copydir.c
 *    copies a directory
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *  While "xcopy /e /i /q" works fine for copying directories, on Windows XP
 *  it requires a Window handle which prevents it from working when invoked
 *  as a service.
 *
 * IDENTIFICATION
 *    src/backend/storage/file/copydir.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>

#include "miscadmin.h"
#include "pgstat.h"
#include "storage/copydir.h"
#include "storage/fd.h"

/*
 * copydir: copy a directory
 *
 * If recurse is false, subdirectories are ignored.  Anything that's not
 * a directory or a regular file is ignored.
 */
void
copydir(char *fromdir, char *todir, bool recurse)
{
    DIR        *xldir;
    struct dirent *xlde;
    char        fromfile[MAXPGPATH * 2];
    char        tofile[MAXPGPATH * 2];

    if (MakePGDirectory(todir) != 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not create directory \"%s\": %m", todir)));

    xldir = AllocateDir(fromdir);

    while ((xlde = ReadDir(xldir, fromdir)) != NULL)
    {
        struct stat fst;

        /* If we got a cancel signal during the copy of the directory, quit */
        CHECK_FOR_INTERRUPTS();

        if (strcmp(xlde->d_name, ".") == 0 ||
            strcmp(xlde->d_name, "..") == 0)
            continue;

        snprintf(fromfile, sizeof(fromfile), "%s/%s", fromdir, xlde->d_name);
        snprintf(tofile, sizeof(tofile), "%s/%s", todir, xlde->d_name);

        if (lstat(fromfile, &fst) < 0)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not stat file \"%s\": %m", fromfile)));

        if (S_ISDIR(fst.st_mode))
        {
            /* recurse to handle subdirectories */
            if (recurse)
                copydir(fromfile, tofile, true);
        }
        else if (S_ISREG(fst.st_mode))
            copy_file(fromfile, tofile);
    }
    FreeDir(xldir);

    /*
     * Be paranoid here and fsync all files to ensure the copy is really done.
     * But if fsync is disabled, we're done.
     */
    if (!enableFsync)
        return;

    xldir = AllocateDir(todir);

    while ((xlde = ReadDir(xldir, todir)) != NULL)
    {
        struct stat fst;

        if (strcmp(xlde->d_name, ".") == 0 ||
            strcmp(xlde->d_name, "..") == 0)
            continue;

        snprintf(tofile, sizeof(tofile), "%s/%s", todir, xlde->d_name);

        /*
         * We don't need to sync subdirectories here since the recursive
         * copydir will do it before it returns
         */
        if (lstat(tofile, &fst) < 0)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not stat file \"%s\": %m", tofile)));

        if (S_ISREG(fst.st_mode))
            fsync_fname(tofile, false);
    }
    FreeDir(xldir);

    /*
     * It's important to fsync the destination directory itself as individual
     * file fsyncs don't guarantee that the directory entry for the file is
     * synced. Recent versions of ext4 have made the window much wider but
     * it's been true for ext3 and other filesystems in the past.
     */
    fsync_fname(todir, true);
}

/*
 * copy one file
 */
void
copy_file(char *fromfile, char *tofile)
{
    char       *buffer;
    int         srcfd;
    int         dstfd;
    int         nbytes;
    off_t       offset;
    off_t       flush_offset;

    /* Size of copy buffer (read and write requests) */
#define COPY_BUF_SIZE (8 * BLCKSZ)

    /*
     * Size of data flush requests.  It seems beneficial on most platforms to
     * do this every 1MB or so.  But macOS, at least with early releases of
     * APFS, is really unfriendly to small mmap/msync requests, so there do it
     * only every 32MB.
     */
#if defined(__darwin__)
#define FLUSH_DISTANCE (32 * 1024 * 1024)
#else
#define FLUSH_DISTANCE (1024 * 1024)
#endif

    /* Use palloc to ensure we get a maxaligned buffer */
    buffer = palloc(COPY_BUF_SIZE);

    /*
     * Open the files
     */
    srcfd = OpenTransientFile(fromfile, O_RDONLY | PG_BINARY);
    if (srcfd < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not open file \"%s\": %m", fromfile)));

    dstfd = OpenTransientFile(tofile, O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
    if (dstfd < 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not create file \"%s\": %m", tofile)));

    /*
     * Do the data copying.
     */
    flush_offset = 0;
    for (offset = 0;; offset += nbytes)
    {
        /* If we got a cancel signal during the copy of the file, quit */
        CHECK_FOR_INTERRUPTS();

        /*
         * We fsync the files later, but during the copy, flush them every so
         * often to avoid spamming the cache and hopefully get the kernel to
         * start writing them out before the fsync comes.
         */
        if (offset - flush_offset >= FLUSH_DISTANCE)
        {
            pg_flush_data(dstfd, flush_offset, offset - flush_offset);
            flush_offset = offset;
        }

        pgstat_report_wait_start(WAIT_EVENT_COPY_FILE_READ);
        nbytes = read(srcfd, buffer, COPY_BUF_SIZE);
        pgstat_report_wait_end();
        if (nbytes < 0)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read file \"%s\": %m", fromfile)));
        if (nbytes == 0)
            break;
        errno = 0;
        pgstat_report_wait_start(WAIT_EVENT_COPY_FILE_WRITE);
        if ((int) write(dstfd, buffer, nbytes) != nbytes)
        {
            /* if write didn't set errno, assume problem is no disk space */
            if (errno == 0)
                errno = ENOSPC;
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not write to file \"%s\": %m", tofile)));
        }
        pgstat_report_wait_end();
    }

    if (offset > flush_offset)
        pg_flush_data(dstfd, flush_offset, offset - flush_offset);

    if (CloseTransientFile(dstfd) != 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not close file \"%s\": %m", tofile)));

    if (CloseTransientFile(srcfd) != 0)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not close file \"%s\": %m", fromfile)));

    pfree(buffer);
}